1. Field of the Invention
The present invention relates to a gain variable amplifier apparatus.
2. Description of the Related Art
A first prior art gain variable amplifier apparatus is formed by a single stage gain variable amplifier. This will be explained later in detail.
In the above-described first prior art gain variable amplifier apparatus, however, the region of linear gain characteristics is narrow, and also, the gain is dependent upon the thermal voltage.
A second prior art gain variable amplifier apparatus is formed by three stages of gain variable amplifiers connected in series (see JP-A-8-46463). The reference voltages of the gain variable amplifiers are made different from each other to obtain a total gain having a wider linear relationship. This also will be explained later in detail.
The above-described second gain variable amplifier apparatus, however, needs a plurality of gain variable amplifiers to achieve a wider gain control range, which would increase the power consumption.